Method and means for punching

ABSTRACT

A method and means for punching includes the use of a resilient washer-like member as a punch tip.

United States Patent Cady, Jr.

15] 3,670,610 1451 June 20, 1972 METHOD AND MEANS FOR PUNCHING Inventor: Percy L. Cady, Jr., Darien Center, NY.

Assignee: Houdaille Industries, Inc., Buffalo, NY.

Filed: Dec. 22, 1969 Appl. No.2 886,986

US. Cl ..83/55, 83/685, 83/686,

83/689 Int. Cl. ..B26f 1/14 Field of Search ..83/68469 l 542,

[56] References Cited UNITED STATES PATENTS 2,258,843 10/1941 Brown ..83/542 x 2,882,971 4/1959 Bennett et al.. .....s3/5ss x 2,772,501 12/1956 Malcolm.... .....83/542 x 3,091,855 6/1963 Hart ..83/621 x FOREIGN PATENTS OR APPLICATIONS 592,179 4/1925 France ..83/620 Primary Examiner-James M. Meister Attorney-Hill, Sherman, Meroni, Gross & Simpson [57] ABSTRACT A method and means for punching includes the use of a resilient washer-like member as a punch tip.

31 Claims, 20 Drawing Figures PATENTEDJum 1212 SHEET 3 BF 3 l N VENTOR.

METHOD AND MEANS FOR PUNCI-IING BACKGROUND This invention pertains to a method and means for punching, and more specifically pertains to the use of a resilient washer-like member as a punch tip.

PRIOR ART SUMMARY OF THE INVENTION The present invention is the provision of or the use of a resilient washer-like member as a punch tip.

Accordingly, it is an object of the present invention to provide an improved method and means for punching.

A further object of the present invention is to provide a punch tip which requires no stripping force to remove it from a workpiece.

A still further object of the present invention is to provide a punch tip which will produce a high-quality hole in a workpiece.

Yet another object of the present invention is to provide a punch tip that will produce a punched hole in a workpiece having negligible taper along the axis of such hole.

A still further object of the present invention is to provide a punch tip that will produce a hole in the workpiece involving a minimum of fracture and a maximum of high quality surface finish.

Another object of the present invention is to provide an inexpensive easily replaceable punchtip.

Many other advantages, features and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which preferred struc tural embodiments incorporating the principles of the present invention are shown by way of illustrative example.

On the drawings:

FIG. I is a fragmentary elevational view, partly in cross section, of a punching machine having embodied therein a punching device in accordance with the principles of the present invention;

FIG. 2 is a side elevational view of a C-frame type of subpress tooling embodying a punching device according to the present invention;

FIG. 3 is an end elevational view of the device of FIG. 2;

FIG. 4 is a fragmentary top view taken along line IVIV OF FIG. 2;

FIG. 5 is a cross-sectional view of a box frame or multiple hole type of sub-press tooling embodying a punching device in accordance with this invention;

Each of FIGS. 6-1 I inclusive illustrate further embodiments of the invention;

FIGS. 12, 13. and 15, appearing with FIG. 1, show still further embodiments thereof, FIGS. 14 and 16 being respectively taken along lines XIV-XIV of FIG. 13 and XVI-XVI ofFIG. and

FIGS. 17-20 each illustrate still further embodiments .of the invention.

As shown on the drawings, the principles of the present invention are particularly useful when embodied in a punching machine such as shown in FIG. 1, generally indicated by the numeral 20. The punching machine 20 includes a conventional die 21 supported on a die ring 22 carried by a bolster 23. The punching machine 20 further includes a reciprocable ram 24 and a tool support arm 25 which is normally stationary. The support arm 25 has an aperture which slidably receives and guides a punch body 26 so that the arm 25 comprises means for guiding the punch body 26 for relative movement toward and away from the die 21. A lifting spring 27, illustrated in partially compressed form, acts between the punch body 26 and the guide means 25 for moving the punch body 26 away from the die 21, the lifting spring 27 being the sole means in this embodiment for restoring the punch body 26 to its uppermost position on retraction of the ram 24. To that end, in this embodiment, the punch body 26 has a shoulder or snap ring 28 against which the lifting spring 27 acts.

According to the present invention, the punch body 26 is provided with a punch tip 29 of sheet-like flexible resilient material and which tip 29 is secured to the punch body 26 by appropriate securing means 30, here comprising a screw.

For convenience, the punch body 26 may be constructed to include a guide portion 31 and a spacer portion 32 held together by the securing means 30 and held against rotation by a key 33. The punch body 26 has an end surface 34 against which the punch tip 29 is disposed.

The punch tip 29 comprises sheet-like flexible resilient material and has a first or lower surface 35 directed toward or facing a workpiece 36. In this embodiment, the surface 35 has a frusto-conical configuration. The punch tip 29 has a second or upper oppositely facing surface 37. The surface 37 has a central portion 38 which engages the central portion of the end surface 34 of the punch body 26. The surface 37 of the punch tip 29 extends radially from the punching axis at least as far as the punch body end surface 34 extends, and preferably extends beyond as shown. The outer peripheral portion 39 of the punch tip 29 is normally spaced from the end surface 34 but is deflectable toward it. The outer peripheral surface 39 extends for at least a majority of the periphery of the punch tip in an axial direction away from the punch body 26 and away from the central portion of the punch tip, and in this embodiment, extends continually in an axially spaced manner along such periphery. With this construction, the punch tip 29 can be said to have a generally concave lower surface 35 and a generally convex surface 37. It is to [be noted that there is a concavity or frusto-conical configuration illustrated for the end surface 34, and where such feature is present, the convexity of the second surface 39 is such that a peripheral gap is provided as illustrated. The angular gap between the punch tip 29 and the punch body 26 both enables deflection of the outer peripheral portion 39 of the punch tip 29 and also limits such deflection. It is preferable that the portion 32 of the punch.

body 26 that might enter a workpiece be of a size smaller than the outside dimensions of the punch tip 29 to facilitate such entry.

When an unpunched workpiece 36 is placed on the die 21 and the ram 24 advances the punch body 26 and the punch tip 29, the lower or outer periphery of the punch tip 29 engages the workpiece 36 which provides a reaction, causing the outer periphery of the punch tip 29 to deflect relatively upwardly with respect to the punch body 26. Where there is sufficient reaction from the workpiece, such deflection is limited by the end surface 34. As soon as deflection begins, the effective outside size or diameter of the punch tip 29 begins to increase and to slide a few thousandths of an inch in a radially outer direction and to thereby increase its effective size. As the punch tip is advanced further, it begins to enter the workpiece 36 and to shear it off. The instant that a slug 36a separates from the workpiece 36, the resilient punch tip 29 snaps to the position illustrated, thus propelling the slug 36a with a positive force through the die 21. At this same moment, the effective size of the punch tip immediately decreases and is for all practical purposes out of contact with either the die 21 or the material of the workpiece 36 that defines the newly made hole. Accordingly, the lifting spring 27 readily comprises the sole means to take the punch tip 29 out of such opening in the workpiece 36.

From the foregoing, it is seen that the present invention further includes the novel method or process which involves the use of a resilient washer-like member as a punch tip.

In the embodiment shown in FIG. 2, the punch tip 29 is secured to a punch body 40 which is slidably guided in a C- frame type of subpress tool holder 41, the body 40 being upwardly biased by a relatively light-duty lifting spring 42. Heretofore, in this type of tooling, a substantial amount of stripping force has been necessary to remove the punch from the workpiece, and the means for providing such stripping force have normally affected the thickness of the tooling in a left-to-right direction as seen in FIG. 3. However, with the present invention, which includes a die 43, secured in the lower arm of the C-frame 41 as by screws 44, the die for first time becomes the limiting factor. If one is to use a removable or separate die button, for a given size hole, there will be a certain amount of material needed in the die button around such hole, for example, as shown in FIG. 4. When tooling is built in accordance with the present invention, no portion of the entire device needs to be as large as the left-to-right dimension of the die 43 as seen in FIG. 3, thereby enabling very close spac ing of such units to other tooling used in association therewith.

Even closer spacing of adjacent punches is enabled by the use of this invention in sub-press tooling of the box-frame or multiple hole type as illustrated in FIG. 5. In this embodiment, the lowermost member 45 comprises die steel wherein the die openings are extremely close to each other, and as will be more fully understood from description which follows, the amount of material between the die openings in this construction and hence the closeness of one hole to be produced to the next, is somewhat less than any portion of the reciprocating components of the punching device. In this embodiment, the punch tip 29 is secured to a punch body 46 which has a reduced rather than enlarged guide portion 47 which is surrounded by a lifting spring 48 acting against a head, shoulder or ring 49 and against the guide means or upper plate 50 as in the previously described embodiments.

FIGS. 6-16 illustrate variations in configuration that can be given to the shape of the punch tip 29. In FIG. 6, there is illustrated a punch tip 51 which has flat upper and lower surfaces and which is secured at its center portion to a punch body 52 having a convex end surface 53.

In FIG. 7, a punch tip 54 is illustrated as having a truly convex upper surface and a truly concave lower surface disposed against a flat end surface 55 on a punch body 56. Note that approximately the same amount of clearance is provided at the peripheral portion of the punch tip 54, but that the degree of concavity is somewhat less than that shown in FIG. 1 since the punch tip 54 coacts with a flat end surface 55.

FIG. 8 illustrates a punch tip 57 which is similar to that of FIG. 7 except that four secant portions have been omitted or removed to provide a non-circular configuration, here, a square. Wherever a non-circular punch tip is employed, means must be provided to prevent unwanted rotation and to assure angular alignment with a die having a similar shape. To that end, a keyway 58 is provided for reception of the key 33 as explained previously.

As illustrated in FIG. 9, as well as in FIG. 10, the punch tip may be constructed so as to have a frusto-pyramidal configuration, a square version of punch tip 59 being shown in FIG. 9 and a rectangular version of punch tip 60 being shown in FIG. 10.

Composites in shape may also be provided for the purpose of punching more complexly shaped holes as illustrated by the punch tip 61 in FIG. 1 1. The circular portion is similar to that of FIG. 7 while the rectangular portion has a configuration substantially like that shown in FIG. 16.

FIG. 12, appearing with FIG. 1, illustrates a punch tip 62 of frusto-conical configuration coacting with the punch body 56 and engaging its flat end surface 55. The punch tip 62 is like the punch tip 29 except that it is somewhat flatter for cooperation with a flat end surface.

A punch tip 63 is illustrated in FIG. 13 which has upper and lower surfaces that are in fact segments of a cylindrical surface. The punch tip 63 thus has a configuration like that of a wave washer as also shown in FIG. 14.

A punch tip 64 shown in FIG. 15 is defined by two intersecting planes and may have any desired peripheral shape, a square shape being here illustrated, the punch tip 64 being further illustrated in FIG. 16. Although the effective diameter will change more than the vertical diameter illustrated, and although the diagonal distance of the punch tip 64 along the section line will change more than the other diagonal distance, I have found that for all practical purposes, these configurations, just like the punch tip 29, need no stripping means to enable their free removal from the workpiece 36.

The embodiment illustrated in FIG. 17 includes a punch body 65 that has an end surface 66 which is generally convex, and which more specifically is a segment of a cylindrical surface. In association therewith, there is a punch tip 63a, similar to the punch tip 63 except that it is provided with a non-circular aperture such as illustrated in other forms. The upper or second surface of the punch tip 63a is also generally convex, and more specifically is a segment of a cylindrical surface. The segments of the cylindrical surfaces of the punch tip 63a and the end surface 66 have axes which are non-parallel to each other and which when the illustrated structure of FIG. 17 is viewed from above, are at right angles to each other. Thus, the periphery of the punch tip 63a undulates with respect to the end surface 66.

The embodiment shown in FIG. 18 is similar to that of FIG. 17 except that a punch body 67 is provided with an end surface 68 which is generally convex, and which more specifically comprises two intersecting planes that intersect at the central portion of a punch tip 64a, which likewise has an upper surface which comprises two planes that intersect at its central portion. Thus, the intersection of the second surface of the punch tip 64a is transverse to the intersection of the end surface 68, and such intersections constitute lines that extend perpendicular to one another and perpendicular to the reciprocation axis of the punching device. Thus, the periphery of the punch tip 64a undulates with respect to the end surface 68.

The embodiment shown in FIG. 19 comprises a punch tip 69, the upper surface of which is illustrated. The punch tip 69 also has a periphery that undulates, and is here provided with two pairs of undulations 70 which are complemental to undulations on the lower side. Thus, the portions 70 are convex as viewed from above and are concave as viewed from below, while the portions 71 are concave as viewed from above and convex as viewed from below. These undulations comprise segments of a conical surface. The term undulation" as used herein has such scope that the illustrated embodiment in FIG. 19 has four undulations on each of its upper and lower surfaces. If desired, the end surface of the punch body may be given a complemental undulation as described above in connection with FIG. 17.

The embodiment of FIG. 20 is similar to that of FIG. 19 except that an odd number of undulations have been provided. An even number is preferred, but an odd number functions satisfactorily.

It is preferable that the outer periphery of the various punch tips 29 etc. illustrated and described herein be parallel to the punching axis. One reason for this is that a whole series of punch tips may be placed on a mandrel and be simultaneously ground or sharpened. A further advantage exists in operation in that when the outer periphery of the punch has been deflected, the punch will have a slightly greater diameter at its lower workpiece-engaging edge than it will at its upper or trailing edge, thereby minimizing drag and provided a slight rake angle.

In all these embodiments, various securing means 30 may be employed. However, where a screw is employed as illustrated, it passes through the aperture in the punch tip and the screw has a head which is substantially flush with the lower or first surface such as 35.

In some applications, it is contemplated that the securing means 30 be omitted to enable the Belleville-washer-like or wave-washer-like punch tip to pass though with the slug 36a.

In an early reduction to practice of this invention, I lifetested a punch tip 29 for about 25,000 cycles or punching operations, and at that time, metallurgical failure of the specimen took place. In that test, the punch tip was one thirtysecond inch thick and had a hardness of Rockwell C51. The diameter was 0.625 inch and the effective amount of bevel or deflection was 4. It was used in association with a die having a total die clearance of 0.010 inch.

In another test, a punch tip 29 of the same construction was used to perforate steel plate one-quarter inch thick with a successive series of total die clearances by using such punch tip with different dies. All of the holes had the same diameter. When the punch was used with a die with a total clearance of 0.006 inch, the hole that was made had an internal surface that was 100 percent shear. As the clearance increased, the hole size remained constant but the percentage of shear decreased. The surface finish of the sheared portion is comparable to that of a broached hole and is of such high quality and smoothness that the same can be used as a preliminary hole-forming means prior to threading.

I have also tested the same punch in association with aluminum having a thickness of 0.015 inch, and the same has operated satisfactorily.

Whenever there is sufficient reaction from the workpiece so as to enable the punch tip 29 to flatten or to otherwise engage the end surface of the punch body in the instance of other shapes, then the hole size that a particular punch tip will make is constant.

The hole size can be reduced considerably from that mentioned in the above tests. For instance, a zfi-in'ch-diameter hole can be made.

The punch tip 29 illustrated in FIG. 1 has about a 6 angle of bevel but the amount of undercut or concavity in the spacer 32 makes the effective angle about 4.

Absolute concentricity between the resilient punch tip 29 and the die 21 is not always necessary from a functional standpoint.

In another test, a punch tip had a free diameter of 0.626 inch and was used with a die that had a hole diameter of 0.662 inch. As the punch tip was flattened out during the punching of the hole, it temporarily grew in effective diameter so that the hole produced was 0.630 inch in diameter, this test having been made in 0.0598-inch steel.

In another test, a punch tip hada free diameter of 2.983 inches and was used with a die that had a-hole diameter of 3.008 inches. As the punch tip was temporarily flattened during the punching of the hole, it grew in effective diameter so that the hole produced was 3.004 inches in diameter, this test having been made in 0.120-inch material. The die clearance involved is 3.3 percent. The holes were entirely satisfactory, and in particular had a shaved or broached appearance for practically 100 percent of the thickness of the material.

In another facet of the preceding test, the same punch was used with a die having a hole diameter of 3.037 inches. In this instance, with 24 percent of the thickness of the workpiece as being die clearance, the hole size was 3.008 inches in the same material. These holes also were satisfactory in all respects.

These last two tests demonstrate the fact that the punch diameter of the relaxed punch tip was 0.021 inch and 0.025 inch less than the size of the hole it produced, and the hole size was in fact determined by the punch and not by the die size. With so much clearance, there is absolutely no stripping force involved. In this instance, the central hole of the punch tip had an inside diameter of 1.22 inches and the punch tip thickness was 0.185 inch.

In another test which involved life testing, the punch tip had a free diameter of 1.500 inches and an inside diameter of eleven-sixteenth inch. The punch tip was made of material having a thickness of 0.050 inch hardened to 55 Rockwell C. In this instance, the outside diameter had been ground to size after removing initial set. A life test was run on cold rolled steel having a thickness of 0.062 inch with a die clearance of 0.012 inch. After 82,000 holes had been punched, there was no failure and the tip had grown 0.001 inch in diameter.

With this structure, a user does not need to resharpen punch tips because punch tips according to the present invention can be produced for about the same cost as a resharpening opera tion. Thus, with this structure, a constant punch length is provided without need for readjustment as is presently the case with tooling that is periodically sharpened. This further enables a constant press stroke. Further, the penetration into the workpiece and the die becomes a constant. In fact, the punch tip 29 does not need to enter the die 21.

With conventional punches, die clearances must be controlled to enable stripping. Thus, with. thick material, relatively large die clearance is needed or it would not be possible to withdraw the punch tip. With thin material, used with conventional punches, a small die clearance is needed. Thus, with conventional construction, depending upon the thickness of material, the user must alter the die that is used in association with a particular punch tip, depending upon the thickness of the material being punched. With the present invention, low clearances can be used for any thickness of material as there is no stripping force required.

With the construction of FIG. 5, it is possible to provide punched holes that are almost tangent to each other.

One of the most important advantages of this invention is that at the time of fracture, the force from the press is instantly reduced, and force is needed only to move the slug through the die. However, there is energy stored in the deflected punch tip tending to return the punch tip to its original shape. Release of this stored energy propels the slug through the die.

The lifting spring may be omitted wherever the punch assembly is secured to the ram, and the only work that the ram has in its return stroke is to lift those components, there being no restraint by the workpiece because the punch tip, in its relaxed or free condition, is smaller than the hole it produced in the workpiece.

Because of the slug ejection force stored in the punch tip, the punch tip does not need to enter the die.

Since alignment of the punch tip and the die is less critical when using low clearances, low clearances are more practical, than before.

The punch tips according to this invention are inexpensive and are light in weight compared to conventional tooling.

When the punch and die of FIG. 1 are removed from the punching machine, only a nominal amount of storage space is necessary since the punch readily nests within the die 21.

This invention has solved a further problem. Fast acting presses equipped with numerically controlled workpiece positioning mechanisms, or coil feed types of presses are subject to malfunction if the slug is withdrawn by the punch tip back into the hole. If that malfunction should take place, the slug would not be flush and this would tend to lock the workpiece to the die. On movement of the positioning mechanism, slippage takes place between the workpiece and whatever structure grips it, whereby dimensional control is lost. With this invention, the action of the punch tip in releasing its stored energy to forcibly eject the slug eliminates the foregoing problem.

Punch tips constructed in accordance with this invention are not only relatively inexpensive to make, but they require somewhat less material. Being small, they are relatively light in weight and are less cumbersome to handle.

Although various minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted herein, all such embodiments as reasonably and properly come within the scope of the appended claims.

I claim:

I. A punching device, comprising:

a. a punch body having an end surface; and

b. a punch tip of sheet-like flexible resilient material having a first surface for being directed toward a workpiece, and a second oppositely facing surface extending radially at least as far as said end surface of said body extends, and having a central portion disposed against said end surface of said punch body, an outer peripheral portion of said second surface being normally spaced from but deflectable toward said end surface of said punch body in response to engagement of said first surface with the workpiece.

2. A punching device according to claim 1, in which said outer peripheral portion is engageable with said end surface by which the deflection thereof is thus limited.

3. A punching device according to claim 1, which includes means disposed at said central portion and securing said punch tip to said body.

4. A punching device according to claim 3, in which said securing means is a screw securing said resilient punch tip to said punch body.

5. A punching device according to claim 4, in which said screw extends through an aperture in said punch tip, said screw having a head substantially flush with said first surface.

6. A punching device according to claim in which said aperture is non-circular, and including keying means acting between said punch tip and said punch body.

7. A punching device according to claim 1 in which said first surface is generally concave and in which said second surface is generally convex.

8. A punching device according to claim 1 in which the edge of said punch tip in its free position is parallel to the axis of said punch body.

9. A punching device according to claim 1 in which said punch tip in its free position is flat, and in which said end surface of said punch body is generally convex.

10. A punching device comprising:

a. a punch body having an end surface;

b. a punch tip of sheet-like flexible resilient material having a first surface for being directed toward a workpiece, and a second oppositely facing surface having a central portion disposed against said end surface of said punch body, an outer peripheral portion of said second surface being normally spaced from but deflectable toward said end surface of said punch body in response to engagement of said first surface with the workpiece;

c. a die disposed in a position for coaction with said punch tip on a workpiece; and a d. means guiding said punch body for relative movemen toward and away from said die.

11. A punching device according to claim 10 including lifting spring means acting between said guiding means and said punch body for effecting said movement away from said die.

12. A punching device according to claim 11 wherein said lifting spring means comprises the only spring means for acting to remove said punch tip from an opening that it has made in the workpiece.

13. A punching device according to claim 1 in which said normally spaced outer portion of said second surface extends continually along the periphery thereof.

14. A punching device according to claim 1 in which at least a majority of the periphery of said punch tip extends in an axial direction away from said punch body and away from the central portion of said punch tip.

15. A punching device according to claim 14 in which said first surface is generally concave.

16. A punching device according to claim 14 in which said first surface is generally frusto-conical.

17. A punching device according to claim 14 in which said first surface is generally frustopyramidal.

18. A punching device according to claim 14 in which said first surface is a segment of a cylindrical surface.

19. A punching device according to claim 14 in which said first surface comprises two intersecting planes.

20. A process of punching sheet metal including the step of using the outer periphery of a Belleville spring as a selfstripping punch tip.

21. A punching device according to claim 1 in which the periphery of the punch tip undulates with respect to said end surface.

22. A punching device according to claim 1 in which said end surface and said second surface are generally convex.

23. A punching device according to claim 1 in which said end surface and said second surface are segments of cylindrical surfaces which have non-parallel axes.

24. A punching device according to claim 23 in which said axes are at right angles to each other.

25. A punching device according to claim 1 in which each of said end surface and said second surface comprises two planes which intersect at said central portion.

26. A punching device according to claim 25 in which the intersection of said second surface is transverse to the intersection of said end surface.

27. A punching device according to claim 26 in which said intersections comprise lines perpendicular to each other.

28. A punching device according to claim 1, in which said first and second surfaces have at least three complemental undulations extending along their peripheries.

29. A punching device according to claim 28 having at least two pairs of said undulations.

30. A punching device according to claim 28 in which said undulations comprise segments of a conical surface.

31. A punching device according to claim 1 in which the shape of said second surface is substantially complemental to the shape of said end surface to provide a continuous peripheral spacing therebetween. 

1. A punching device, comprising: a. a punch body having an end surface; and b. a punch tip of sheet-like flexible resilient material having a first surface for being directed toward a workpiece, and a second oppositely facing surface extending radially at least as far as said end surface of said body extends, and having a central portion disposed against said end surface of said punch body, an outer peripheral portion of said second surface being normally spaced from but deflectable toward said end surface of said punch body in response to engagement of said first surface with the workpiece.
 2. A punching device according to claim 1, in which said outer peripheral portion is engageable with said end surface by which the deflection thereof is thus limited.
 3. A punching device according to claim 1, which includes means disposed at said central portion and securing said punch tip to said body.
 4. A punching device according to claim 3, in which said securing means is a screw securing said resilient punch tip to said punch body.
 5. A punching device according to claim 4, in which said screw extends through an aperture in said punch tip, said screw having a head substantially flush with said first surface.
 6. A punching device according to claim 5 in which said aperture is non-circular, and including keying means acting between said punch tip and said punch body.
 7. A punching device according to claim 1 in which said first surface is generally concave and in which said second surface is generally convex.
 8. A punching device according to claim 1 in which the edge of said punch tip in its free position is parallel to the axis of said punch body.
 9. A punching device according to claim 1 in which said punch tip in its free position is flat, and in which said end surface of said punch body is generally convex.
 10. A punching device comprising: a. a punch body having an end surface; b. a punch tip of sheet-like flexible resilient material having a first surface for being directed toward a workpiece, and a second oppositely facing surface having a central portion disposed against said end surface of said punch body, an outer peripheral portion of said second surface being normally spaced from but deflectable toward said end surface of said punch body in response to engagement of said first surface with the workpiece; c. a die disposed in a position for coaction with said punch tip on a workpiece; and d. means guiding said punch body for relative movement toward and away from said die.
 11. A punching device according to claim 10 including lifting spring means acting between said guiding means and said punch body for effecting sAid movement away from said die.
 12. A punching device according to claim 11 wherein said lifting spring means comprises the only spring means for acting to remove said punch tip from an opening that it has made in the workpiece.
 13. A punching device according to claim 1 in which said normally spaced outer portion of said second surface extends continually along the periphery thereof.
 14. A punching device according to claim 1 in which at least a majority of the periphery of said punch tip extends in an axial direction away from said punch body and away from the central portion of said punch tip.
 15. A punching device according to claim 14 in which said first surface is generally concave.
 16. A punching device according to claim 14 in which said first surface is generally frusto-conical.
 17. A punching device according to claim 14 in which said first surface is generally frusto-pyramidal.
 18. A punching device according to claim 14 in which said first surface is a segment of a cylindrical surface.
 19. A punching device according to claim 14 in which said first surface comprises two intersecting planes.
 20. A process of punching sheet metal including the step of using the outer periphery of a Belleville spring as a self-stripping punch tip.
 21. A punching device according to claim 1 in which the periphery of the punch tip undulates with respect to said end surface.
 22. A punching device according to claim 1 in which said end surface and said second surface are generally convex.
 23. A punching device according to claim 1 in which said end surface and said second surface are segments of cylindrical surfaces which have non-parallel axes.
 24. A punching device according to claim 23 in which said axes are at right angles to each other.
 25. A punching device according to claim 1 in which each of said end surface and said second surface comprises two planes which intersect at said central portion.
 26. A punching device according to claim 25 in which the intersection of said second surface is transverse to the intersection of said end surface.
 27. A punching device according to claim 26 in which said intersections comprise lines perpendicular to each other.
 28. A punching device according to claim 1, in which said first and second surfaces have at least three complemental undulations extending along their peripheries.
 29. A punching device according to claim 28 having at least two pairs of said undulations.
 30. A punching device according to claim 28 in which said undulations comprise segments of a conical surface.
 31. A punching device according to claim 1 in which the shape of said second surface is substantially complemental to the shape of said end surface to provide a continuous peripheral spacing therebetween. 